1. Field of the Invention
The present invention relates to a heating unit for use in a heater or drier, and more particularly to a device for heating fluid, in which is incorporated a heating unit having positive temperature coefficient PTC semiconductors for heating fluid passing thereby.
2. Description of Prior Art
Such PTC semiconductors can be employed as a heating means, in which electrical energy is converted into thermal energy. When a suitable voltage is applied to the PTC semiconductors material, such as a thermistor, the current flowing therethrough is comparatively high at an initial stage, so that the PTC semiconductor material is heated rapidly up to a certain temperature, which is in relation to the applied voltage. Thereafter, the current drops to a low value to reduce heat generation from the PTC semiconductor, thus maintaining a predetermined temperature.
It is known to use above described PTC semiconductor in the heaters for a heating unit, in which fluid such as air or liquid to be heated passes closely by the PTC semiconductor, thus obtaining heat therefrom.
Referring to FIG. 1, showing a conventional type of heating unit a, in which a plurality of PTC semiconductor heating elements b are aligned in parallel and spaced relation to each other and are supported by four corner bars c1 to c4. Each PTC semiconductor heating element b comprises a PTC semiconductor heating body d having rectangular shaped and parallel opposing faces and a pair of electrodes e1 and e2 provided at opposite edges of the PTC semiconductor heating body d, as most clearly seen in FIG. 2. Since the corner bars are made of electrically conductive material, the corner bars c1 and c2 electrically connect respective electrodes, say electrodes e1, while the corner bars c3 and c4 electrically connect the other electrodes e2. When a suitable voltage is applied between the electrodes e1 and e2 through the corresponding corner bars, the electrical current flows through the PTC semiconductor heating body d both in the inner region and at the outer region of the PTC semiconductor heating body d, thus energizing the whole PTC semiconductor heating body d to generate heat therefrom. Therefore, it is considered that the heat to be emitted from the PTC semiconductor heating body d is generated at the center o, thereof, as shown in FIG. 3. In other words, a heat generating origin x coincides with the center o. Since the generated heat is only emitted from the outer surface of the PTC semiconductor heating body d, it is preferable to have the heat generating origin x on the surfaces of the PTC semiconductor heating body d for rapidly emitting heat from the PTC semiconductor heating element b rapidly responding to the ambient temperature.